xhci: don't use the same variable for stopped and halted rings current TD

Endpoints halted on errors, and endpoints stopped manually both used
the same ep->stopped_td to store the halted or stopped td. this causes
confusion and possible races.

There is no longer a need to use the ep->stopped_td variable to store
the halted TD. A halted endpoint is handled immediately and we can pass
it to the handling function directly.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>